Chemically Resistant Glass Composition For The Manufacture Of Glass Reinforcing Strands

ABSTRACT

The present invention relates to a chemically resistant glass composition for the production of reinforcing strands which comprises the following constituents within the limits defined below, expressed in mol %: SiO 2  67-72%; ZrO 2  5-9.5%, preferably ≧7.5%; R 2 O (R=Na, K and Li) 11-17%; Li 2 O 0-5.5%; K 2 O 0-5.5%; Na 2 O&lt;10%; and CaO 3-9%, the composition furthermore containing less 1% of impurities (Al 2 O 3 , Fe 2 O 3 , Cr 2 O 3 , TiO 2 , MgO, SrO, BaO and P 2 O 5 ) and being free of F. It also relates to the glass strands obtained from this composition and to the composites based on an organic or inorganic material containing such strands.

The invention relates to a chemically resistant glass composition, inparticular one having a high hydrolytic resistance, for the productionof glass reinforcing strands, and to the organic and Inorganic products(or composites) containing such strands.

It has been known for a long time to use glass strands to reinforceorganic and inorganic materials so as to give them better mechanicalproperties. Usually, the strands consist of a glass with the compositionSiO₂—Al₂O₃—CaO—B₂O₃ (called E-glass) that exhibits excellent hydrolyticand thermal resistance. However, this type of glass is not suitable foruse in an alkaline medium, or in an acid medium.

One means of improving the alkaline resistance consists in incorporatingzirconium oxide ZrO₂ into the glass composition. For example, it isknown to use glass with a high ZrO₂ content to reinforce cements, thebasic character of which is very pronounced (pH possibly ranging up to12.5).

Numerous patents disclose glass compositions having a high ZrO₂ content.

EP 0500325 A1 describes compositions for chemically resistant glassfibers that can be used as reinforcements in cement or in plastics. Thecompositions have, in mol %, a TiO₂ content of 5 to 18%, a TiO₂+ZrO₂content of between 12 and 25%, a BaO content of 4 to 15% and an MgO,CaO, SrO, BaO and ZnO content of between 12 and 35%.

JP 9156957 describes fiber made of glass resistant to alkalis, to acidsand to water, which comprises 5 to 9 mol % TiO₂ and possesses a TiO₂ andZrO₂ content of between 13 and 17 mol %.

U.S. Pat. No. 5,064,785 B discloses an alkaline-resistant glasscomposition for glass fibers, which contains 10 to 17 wt % Na₂O and 0.5to 7 wt % TiO₂.

JP 2000-186787 A describes a pipe (or tube) made of resin reinforced byfibers of glass resistant to alkalis and to acids, which contains 10 to17 wt % Na₂O.

WO 2004/035497 A1 describes fibers consisting of a glass compositioncomprising, in mol %, 50 to 60% SiO₂, 0.5 to 20% TiO₂, 20 to 45% MgO,CaO, SrO and BaO and 0 to 2% Li₂O, Na₂O and K₂O, and having a BaO/CaOmolar ratio between 0.3 and 16.

U.S. Pat. No. 6,627,569 B and U.S. Pat. No. 6,630,420 B disclose glasscompositions containing, in wt %, 0.5 to 7% Al₂O₃, less than 10% Na₂Oand K₂O and more than 0.1% TiO₂ or more than 0.6% La₂O₃.

CN 1046147 A describes fiber made of alkaline-resistant glass comprising11 to 14 wt % ZrO₂ and 1 to 5.5 wt % TiO₂.

CN 1149031 A describes fiber made of alkaline-resistant glass containing0.1 to 10 wt % TiO₂ and 0.1 to 5 wt % CaF₂.

U.S. Pat. No. 4,014,705 B discloses continuous fibers made ofalkaline-resistant glass containing 3 to 9 mol % F₂.

Apart from their alkaline resistance, glasses having a high ZrO₂ contentgenerally exhibit good acid resistance.

Strands consisting of a glass having a high proportion of ZrO₂ that canbe used to reinforce cement are sold under the trademark Cern-FIL®. Theymay also be used to reinforce polymer matrices, particularly polyesterand vinyl ester polymers, in composites intended for being in contactwith acid media (WO 2006/090030 A1).

One drawback of the aforementioned glass strands is their hydrolyticsensitivity. The Applicant has in fact found that the materials andcomposites reinforced by these strands lose their mechanical strengthwhen aged in a wet medium, in particular at high temperatures. In thecase of composites with a polymer matrix, the glass strands no longeradhere properly to the matrix, this being manifested by whitening of thecomposite. Without wishing to be tied down by any particular theory, itseems that the whitening is due to exchange between the Na⁺ ions presenton the surface of the glass and the protons contained in the aqueousmedium. This causes degradation of the surface structure of the glassand, subsidiarily, a local increase in the proportion of OH⁻ ions thatfavors rupture of the chemical bonds between the glass and the matrix.The amount of whitening is directly linked to the amount of Na₂O in theglass composition.

It is the object of the present invention to provide a chemicallyresistant glass composition which has in particular an improvedhydrolytic resistance, while still maintaining good resistance to acidsand alkalis, and which may be processed under the usual conditions inexisting fiberizing installations.

This object is achieved thanks to a chemically resistant glasscomposition for the production of strands, this composition beingcharacterized in that it comprises the following constituents within thelimits defined below, expressed in mol %:

SiO₂ 67-72% ZrO₂ 5-9.5%, preferably ≧7.5% R₂O (R = Na, K and Li) 11-17%Li₂O  0-5.5% K₂O  0-5.5% Na₂O   <10% CaO   3-9%,the composition furthermore containing less than 1% of impurities(Al₂O₃, Fe₂O₃, Cr₂O₃, TiO₂, MgO, SrO, BaO and P₂O₅) and being free of F.

According to one feature of the invention, the glass compositionsatisfies the following relationship:

2.5%≦Na₂O+K₂O—CaO≦9.5%,

thereby making it possible to guarantee that the fiberizing takes placeunder satisfactory conditions, that is to say that the differencebetween the strand forming temperature (T_(logη=3)) and the liquidustemperature (T_(liq)) is at least +10° C. Preferably, the difference isat least +30° C. and advantageously at least +60° C.

Furthermore, the forming temperature is at most 1320° C. and ispreferably 1300° C. or below, this corresponding to a temperature thatis very acceptable as it does not require the glass to be excessivelyheated and makes it possible to minimize bushing wear.

The preferred glass composition according to the invention comprises thefollowing constituents (in mol %):

SiO₂ 67-72% ZrO₂ 5-9.5%, preferably ≧7.5% R₂O (R = Na, K and Li) 11-17%Li₂O  0-5.5% K₂O 2.5-5.5%  Na₂O 5-<10% CaO   3-9%,the composition furthermore containing less than 1% of impurities(Al₂O₃, Fe₂O₃, Cr₂O₃ and P₂O₅) and being free of F, TiO₂, MgO, SrO andBaO.

The particularly preferred glass composition according to the inventioncomprises the following constituents (in mol %):

SiO₂ 67-72% ZrO₂ 5-8.5%, preferably ≧7.5% R₂O (R = Na, K and Li) 11-17%Li₂O 1.5-5.5%  K₂O 2.5-5.5%  Na₂O 5-<10% CaO   3-9%,the composition furthermore containing less than 1% of impurities(Al₂O₃, Fe₂O₃, Cr₂O₃ and P₂O₅) and being free of F, TiO₂, MgO, SrO andBaO.

According to yet another feature of the invention, the CaO content inthe glass composition varies from 3 to 8.5%.

SiO₂ is the oxide that forms the network of the glass according to theInvention and plays an essential role in stabilizing it. Within thecontext of the invention, when the SiO₂ content is less than 67%, theviscosity of the glass becomes too low and there is a greater risk ofthe glass devitrifying during fiberizing. In general, the SiO₂ contentis kept at 72% or below, as above this value the glass becomes tooviscous and difficult to melt. Preferably, the SiO₂ content varies from68 to 71.5%. Furthermore, SiO₂ contributes to improving the resistancein a neutral or acid medium.

ZrO₂ is essential for giving the glass alkaline resistance, and itscontent is consequently at least about 5%, preferably 7.5% or higher.Furthermore, ZrO₂ helps to improve the acid resistance. A ZrO₂ contentgreater than 9.5% increases the risk of devitrification duringfiberizing and degrades the fusibility.

Na₂O, K₂O and Li₂O are used as fluxing agents to lower the viscosity ofthe glass and to allow better dissolution of the ZrO₂ during the meltingof the glass batch.

Na₂O has a deleterious effect on the hydrolytic resistance of the glassand consequently its content is limited to a value of 10% or less, butpreferably greater than 5%, again to maintain satisfactory melting andfiberizing conditions.

The Li₂O and K₂O contents are preferably less than 5.5% so as tomaintain an acceptable liquidus temperature and to minimize the cost ofthe glass (Li₂O-based and K₂O-based raw materials are generallycarbonates, which are costly).

A K₂O content of greater than 2.5% is preferred.

Preferably, the glass composition contains Li₂O and K₂O, therebyreducing the leaching of alkaline metals (Na, K and/or Li) when theglass is in contact with an aqueous medium. An advantageous level ofleaching is obtained when the Li₂O content is greater than 1.5%,preferably around 2%.

According to one advantageous feature of the invention, the Li₂O/R₂O andK₂O/R₂O molar ratios are equal to 0.5 or less. Preferably, LiO₂/R₂O is0.35 or less and K₂O/R₂O is 0.30 or less.

According to the invention, the R₂O content, that is to say the sum ofthe Na₂O, K₂O and Li₂O contents, is 11% or more and preferably less than17% so as to have satisfactory melting and fiberizing conditions.

CaO allows the viscosity of the glass to be adjusted and thedevitrification to be controlled. The CaO content varies between 3 and9% so as to maintain an acceptable liquidus temperature, as a generalrule below 1280° C., preferably below 1260° C. and advantageously 1220°C. or below. Preferably, the CaO content is less than 8.5%. CaOcontributes to improving the hydrolytic resistance of the glasscompositions according to the invention.

The glass composition according to the invention may contain up to 1% ofunavoidable impurities introduced by the batch materials used to producethe glass and/or coming from the refractories of the furnace. Theimpurities consist of Al₂O₃, ion oxides (expressed in Fe₂O₃ form),Cr₂O₃, TiO₂, MgO, SrO, BaO and P₂O₅. The Al₂O₃ content is generally lessthan 0.5%. Preferably, the Fe₂O₃ content does not exceed 0.5% so as notto unacceptably impair the color of the glass strands and the operationof the fiberizing installation, in particular the heat transfer in thefurnace. Also preferably, the Cr₂O₃ content is less than 0.05% andbetter still it is zero. Advantageously, the content of each oxide,TiO₂, MgO, SrO and BaO, is less than 0.5%.

As a general rule, the glass composition contains no TiO₂, MgO, SrO andBaO.

The glass composition is free of F. The presence of fluorine isproscribed because of the risk of polluting emissions and of anexothermic reaction with Li₂O, which may occur during melting, andproblems of the refractory elements of the furnace corroding.

The glass strands are obtained from the glass composition describedabove using the following fiberizing process: a multiplicity of moltenglass streams, flowing out from a multiplicity of holes placed in thebase of one or more bushings, are attenuated in the form of one or moresheets of continuous filaments and then the filaments are gatheredtogether into one or more strands that are collected on a movingsupport. This may be a rotating support when the strands are collectedin the form of wound packages, or in the form of a support that movestranslationally when the strands are chopped by a device that alsoserves to draw them or when the strands are sprayed by a device servingto draw them, so as to form a mat.

The strands obtained, optionally after further conversion operations,may thus be in various forms: continuous strands, chopped strands, wovenfabrics, knitted fabrics, braids, tapes or mats, these strands beingcomposed of filaments having a diameter that may range from about 5 to30 microns.

The molten glass feeding the bushings is obtained from pure rawmaterials or, more usually, natural raw materials (that is to saypossibly containing trace impurities), these raw materials being mixedin appropriate proportions, and then melted. The temperature of themolten glass is conventionally regulated so as to allow the glass to befiberized and to avoid devitrification problems. Before the filamentsare combined in the form of strands, they are generally coated with asize composition with the aim of protecting them from abrasion andallowing them to be subsequently incorporated into the materials to bereinforced. The size composition may be an aqueous or anhydrouscomposition (containing less than 5% solvent by weight), for example thecomposition described in WO 01/90017 A and FR 2837818 A. Whereappropriate, before and/or after collection, the strands may undergo aheat treatment for the purpose of drying them and/or of curing the size.

The glass strands obtained may thus be used to reinforce inorganicmaterials, such as cementitious materials, and organic materials,particularly plastics.

The inorganic materials that can be reinforced are especiallycementitious materials, such as cement, concrete, mortar, gypsum, slagand compounds formed by the reaction between lime, silica and water, andmixtures of these materials with other materials, for example mixturesof cement, polymers and fillers (coatings).

The reinforcement may be carried out directly by incorporating the glassstrands into the cementitious material, or indirectly using glassstrands combined beforehand with an organic material, for example toform composite elements that can be used as rebars for reinforcedconcrete.

The organic materials that can be reinforced by the glass strandsaccording to the invention are thermoplastics or thermosets, preferablythermosets.

As examples of thermoplastics, mention may be made of polyolefins, suchas polyethylene, polypropylene and polybutylene, polyesters, such aspolyethylene terephthalate and polybutylene terephthalate, polyamides,polyurethanes and blends of these compounds.

As examples of thermosets, mention may be made of polyesters, forexample vinyl ester resins, phenolic resins, epoxy resins, polyacrylicsand blends of these compounds. Vinyl ester resins, particularly of theisophthalic type are preferred as they have better corrosion resistance.

As already indicated above, it is possible to use the glass strands inthe form of continuous strands (for example in the form of cakes orrovings, meshes, fabrics, etc.) or chopped strands (for example in theform of nonwovens, such as veils or mats), and their presentationdepends on the nature of the material to be reinforced and on theprocess employed.

Continuous glass strands according to the invention may thus be used formanufacture of hollow bodies, such as pipes or tanks using the knowntechnique of filament winding, which consists in depositing areinforcement, for example a layer of roving impregnated with organicmaterial, on a mandrel rotating about its axis. Such hollow bodies areintended in particular for collecting and discharging wastewater (aspipes) and for storing or transporting chemicals (as tanks andcontainers). As regards chopped strands, these are suitable forreinforcing paints or mastics and for producing composites by contactmolding.

Wound packages of strands may be used for producing meshes or fabricsused as crack-resistant or earthquake-resistant elements in cementitiousmaterials, or for repairing civil engineering works (bridges, tunnels,roads, etc.). The packages may also be used for manufacturing compositesections by pultrusion, that is to say by passing a reinforcementimpregnated with organic material through a heated die. These compositesections are used in particular as construction elements in industrieswhere the materials must have a high resistance to alkalis and acids,for example in the chemical, oil and harbor industries.

The glass strands are generally incorporated into the inorganic ororganic material to be reinforced in an amount such that the glassrepresents 16 to 80% by volume, preferably 20 to 60% by volume, of thefinal material.

In the final composite, the glass strands may be the only elements forreinforcing the inorganic or organic material, or they may be combinedwith other elements, such as metal wires and/or mineral, especialceramic, strands.

The glass composition according to the invention makes it possible toproduce glass strands having a better hydrolytic resistance than theknown strands for reinforcing organic or inorganic materials, and can beinexpensively fiberized in conventional installations without theoperating conditions being modified.

Furthermore, it has been found that these glass strands exhibit gooddielectric properties, especially a dielectric constant ε′ of less than8 at 1 MHz and less than 6.5 at 10 GHz, and dielectric losses ε″ of lessthan 0.0500 at 1 MHz and less than 0.1250 at 10 GHz.

The examples that follow allow the invention to be illustrated withouthowever limiting it.

a) Production of the Glass

Glass was prepared by melting the compositions given in Table 1,expressed in mol %.

The density, Young's modulus, dielectric constant ε′ and dielectriclosses ε″ at 1 MHz and 10 GHz (Table 1) were measured on this glass whencut and polished.

b) Production of the Strands

Glass strands 10 μm in diameter were formed by attenuating molten glassstreams obtained under a) flowing from a platinum bushing and collectedin the form of a bobbin.

The hydrolytic resistance was measured on the glass strand under thefollowing conditions: 60 mg of strand extracted from the above bobbinwere placed in a container holding 9 ml of ultrapure water, thecontainer was then hermetically sealed and placed in a bath thermostatedat 80° C. for 48 hours. The test was carried out on five specimens ofthe same strand. At the same time, three controls each containing only 9ml of ultrapure water were produced.

The content of the five specimens containing the glass strand (solutionS1) and of the three controls (solution S2) were collected and theamount of alkali metal elements in the solutions was measured byinductively coupled plasma (ICP) emission spectroscopy in the case of Naand K and by atomic emission spectroscopy (AES) in the case of Li. Theresulting alkali metal content due to leaching from the glass(corresponding to the difference in contents in S1 and 82), expressed inmol/m³, is given in Table 1 below.

TABLE 1 EXAMPLE 1 2 3 4 5 6 7 8 9 SiO₂ 68.2 71.5 70.5 69.3 69.9 70.769.2 69.1 70.1 Li₂O 3.9 5.2 4.4 2.0 2.9 3.9 2.0 2.2 2.2 Na₂O 7.9 6.3 5.69.8 9.8 7.9 8.8 8.0 8.0 K₂O 3.9 4.2 3.7 3.9 2.9 3.9 3.9 3.5 3.5 CaO 6.83.5 6.5 5.7 5.2 4.3 6.9 8.0 8.0 ZrO₂ 8.9 8.9 8.9 8.9 8.9 8.9 8.9 8.9 7.9R₂O 15.7 15.7 13.7 15.7 15.6 15.7 14.7 13.7 13.7 Na₂O + K₂O − CaO 5 72.8 8.0 7.5 7.5 5.8 3.5 3.5 Li₂O/R₂O 0.248 0.330 0.321 0.127 0.185 0.2480.136 0.160 0.160 K₂O/R₂O 0.248 0.267 0.270 0.248 0.185 0.248 0.2650.255 0.255 T_(logη=3) (° C.) 1251 1295 1293 1292 1289 1291 1286 12881286 T_(liq) (° C.) 1190 1200 1280 1110 1150 1150 1150 1240 n.d.T_(logη=3) − T_(liq) (° C.) 61 95 13 182 139 141 136 48 n.d. Propertiesof the glass Density 2.73 2.69 2.65 2.72 2.71 2.70 2.73 2.74 n.d.Young's modulus (GPa) 88.6 88.5 n.d. 86.8 88.1 87.8 87.1 88.3 n.d. ε′ at1 MHz n.d. n.d. n.d. 7.84 n.d. 7.61 n.d. n.d. n.d. at 10 GHz n.d. n.d.n.d. 6.34 n.d. 6.27 n.d. n.d. n.d. ε″ at 1 MHz n.d. n.d. n.d. 0.0409n.d. 0.0363 n.d. n.d. n.d. at 10 GHz n.d. n.d. n.d. 0.1125 n.d. 0.0990n.d. n.d. n.d. Hydrolytic resistance Na (mol/m³) 0.24 0.28 0.21 0.380.49 0.33 0.21 0.13 0.20 Na + Li + K (mol/m³) 0.38 0.57 0.41 0.52 0.660.54 0.27 0.19 0.28 EXAMPLE 10 11 12 13 14 15 SiO₂ 68.2 68.2 68.2 68.268.2 62.5 Li₂O 3.9 7.9 — — — 2.7 Na₂O 11.8 7.9 11.8 7.9 15.7 13.4 K₂O —— 3.9 7.9 — 3.5 CaO 6.8 6.8 6.8 6.8 6.8 0.7 ZrO₂ 8.9 8.9 8.9 8.9 8.910.6 R₂O 15.7 15.8 15.7 15.8 15.7 16.9 Na₂O + K₂O − CaO 5.0 1.1 8.9 9.96.8 16.2 TiO₂ — — — — — 3.5 Li₂O/R₂O 0.248 0.500 — — — 0.159 K₂O/R₂O — —0.248 0.500 — 0.207 T_(logη=3) (° C.) 1236 1205 1297 1313 1190 1241T_(liq) (° C.) 1230 1320 1160 1350 1190 1170 T_(logη=3) − T_(liq) (° C.)6 −115 137 −37 99 71 Properties of the glass Density 2.73 2.73 2.74 2.722.72 2.83 Young's modulus (GPa) n.d. n.d. n.d. n.d. 79.3 89.0 ε′ at 1MHz n.d. n.d. n.d. n.d. n.d. n.d. at 10 GHz n.d. n.d. n.d. n.d. n.d.n.d. ε″ at 1 MHz n.d. n.d. n.d. n.d. n.d. n.d. at 10 GHz n.d. n.d. n.d.n.d. n.d. n.d. Hydrolytic resistance Na (mol/m³) n.d. n.d. 0.69 n.d.0.90 0.79 Na + Li + K (mol/m³) n.d. n.d. 0.75 n.d. 0.91 0.93 n.d. = notdetermined.

Examples 1 to 9 are in accordance with the invention.

Examples 10 to 15 are comparative examples:

-   -   the glasses of examples 10, 11 and 13 contain a high proportion        of Na₂O, K₂O and Li₂O respectively: these glasses cannot be        fiberized under the usual fiberizing conditions because they        have a (T_(logη=3)−T_(liq)) value that is zero or negative;    -   the glass of example 12 contains a high proportion of Na₂O: it        can be fiberized, especially because it has a suitable K₂O        content and a suitable CaO content, but the strands obtained        have a low hydrolytic resistance; and    -   examples 14 and 15 correspond to compositions of        cement-reinforcing glass strands sold by Saint-Gobain Vetrotex        under the name Cern-FIL° and by NEG under the name ARG®        respectively. The hydrolytic resistance of these strands remains        limited.

The glass strands according to the invention (examples 1 to 9) exhibitexcellent hydrolytic resistance compared with the glass strands having ahigh Na₂O content (example 12) and compared with commercial strands(examples 14 and 15). This is because the observed diffusion of Na⁺ ionsinto the aqueous medium is less than with the known strands: thereduction is equal to 38% and 45% in the case of the least resistantstrands (example 5 compared with examples 15 and 14, respectively) andis equal to 83% and 85% in the case of the most resistant strands(example 8 compared with examples 15 and 14, respectively).

c) Production of the Composites

Strands composed of 17 μm diameter glass filaments were obtained byattenuating molten glass streams of composition according to examples 1,4 and 14 and collected in the form of wound packages. Along their path,the filaments were coated with a conventional aqueous size A (asdescribed in comparative example 2 of FR 2 837 818 A) or with a size Bsuitable for corrosive media (as described in example 1 of FR 2 837 818A) before being collected into strands containing 400 filaments. Thewound packages were dried at 130° C. for 12 hours.

The glass strands were used to form composite sheets containing parallelstrands in accordance with the ISO 1268-5 standard. The reinforced resinwas an isophthalic polyester resin (reference “Synolite 1717” sold byDSM) to which 1.5 parts of hardener (reference “Trigonox HM”, sold byAkzo) per 100 parts of resin by weight were added.

Each sheet contained 50% glass by volume and had a thickness of 3 mm.The sheets were then treated at 80° C. for 2 hours and then at 120° C.for 4 hours in order to accomplish complete crosslinking of the resin.

The following properties were determined on the sheets:

-   -   the Young's modulus according to the ISO 14125 standard and the        Young's modulus of the glass strand M_(atrand) was calculated        using the equation:

M _(strand) =[M _(sheet)−(M _(resin) ×VF _(resin))]/VF _(glass)

in which:

-   -   M_(sheet) is the Young's modulus of the strand composite sheet,        in MPa;    -   M_(resin) is the Young's modulus of the resin, in MPa;    -   VF_(resin) is the volume fraction of the resin in the sheet; and    -   VF_(glass) is the volume fraction of the glass in the sheet.    -   hydrolytic resistance

The sheet was placed in a both of boiling water for 72 hours and, atregular intervals, removed from the bath, drained and weighed. The wateruptake of the composite sheet is equal to the percentage of waterabsorbed by this same sheet over a time interval divided by the squareroot of the time interval, expressed in hours.

-   -   acid resistance

The sheets were protected at the edges by a layer of epoxy resin 1 to 2mm in thickness and then each sheet was placed under a given constantstress, in three-point bending, in an acid solution (1N HCl at 25° C.).The failure time of the composite under the flexural stress conditions(ISO 14125 standard) was measured and the curve of the flexural fracturestrength as a function of time plotted. The value of the SC (StressCorrosion) stress in bending, in MPa, needed to make the composite failafter 100 hours of aging was determined from this curve.

The measured values of the tensile strength and the Young's modulus ofthe glass strand, and also the hydrolytic resistance and acidresistance, of the composite are given in Table 2 below.

TABLE 2 EXAMPLE 16 17 18 19 20 21 22 Strand Glass Ex. 1 Ex. 4 Ex. 14E-glass Ex. 1 Ex. 4 Ex. 14 Size A A A A B B B Tensile strength (N/tex)0.38 0.38 0.29 0.45 0.50 0.45 0.47 Young's modulus (MPa) 72500 7500071500 73000 76000 76000 71500 Composite sheet Water uptake (%/{squareroot over (time (in h)))} n.d. n.d. n.d. 0.03 0.10 n.d. 0.16 SC stress(MPa) 950 1000 n.d. 200 1050 n.d. 850 n.d. = not determined.The strands according to the invention (examples 16 and 17) coated withsize A have a higher tensile strength than the commercial strands(example 18), but this remains below that of the E-glass strands(example 19). The Young's modulus of these strands is higher than thestrands of examples 18 and 19.

The composite sheet containing these strands also has a betterresistance in acid media than that containing E-glass strands (example19).

The same strands coated with size B (examples 20 and 21) have a tensilestrength equivalent to and a Young's modulus greater than those of theknown strands (example 22).

The composite sheets containing the strands according to the inventionexhibit better resistance to aqueous and acid media: the water uptake isreduced and the SC stress is improved compared with those obtained withthe strands of example 22.

1. A chemically resistant glass composition for the production ofreinforcing strands, comprising in mol %: 67-72% SiO₂ 5-9.5% ZrO₂ 11-17%R₂O where R₂O is Na₂O, K₂O and Li₂O 0-5.5% Li₂O 0-5.5% K₂O less than 10%Na₂O 3-9% CaO less than 1% of impurities selected from the groupconsisting of Al₂O₃, Fe₂O₃, Cr₂O₃, TiO₂, MgO, SrO, BaO and P₂O₅; and thecomposition being free of F.
 2. The composition of claim 1, wherein theamounts of Na₂O, K₂O and CaO satisfy the following relationship:2.5%≦Na₂O+K₂O—CaO≦9.5%.
 3. The composition of claim 1 wherein, thedifference between the strand forming temperature (T_(logn=3)) and theliquidus temperature (T_(liq)) is at least +10° C.
 4. The composition ofclaim 1, further comprising: 2.5-5.5% K₂O, and 5-<10% Na₂O.
 5. Thecomposition of claim 4, further comprising: 1.5-5.5% Li₂O.
 6. Thecomposition of claim 1, further comprising: 3 to 8.5% CaO.
 7. Thecomposition of claim 1, wherein the Li₂O/R₂O and K₂O/R₂O molar ratiosare ≦0.5.
 8. The composition of claim 7, wherein the Li₂O/R₂O molarratio is ≦0.35. 9.-14. (canceled)
 15. The composition of claim 1,further comprising about 7.5% ZrO₂.
 16. The composition of claim 7,wherein the K₂O/R₂₀ molar ratio is ≦0.30.
 17. A glass fiber reinforcedcomposite material, comprising: a matrix material; and reinforcingfibers formed of: 67-72 mol % SiO₂; 5-9.5 mol % ZrO₂; 11-17 mol % R₂Owhere R₂O is Na₂O, K₂O and Li₂O; 0-5.5 mol % Li₂O; 0-5.5 mol % K₂O; lessthan 10 mol % Na₂O; 3-9 mol % CaO; less than 1% of impurities (Al₂O₃,Fe₂O₃, Cr₂O₃, TiO₂, MgO, SrO, BaO and P₂O₅); and being substantiallyfree of F.
 18. The glass fiber reinforced composite material of claim17, wherein the amounts of Na₂O, K₂O and CaO satisfy the followingrelationship:2.5%≦Na₂O+K₂O—CaO≦9.5%.
 19. The glass fiber reinforced compositematerial of claim 17, wherein the difference between the strand formingtemperature (T_(logn=3)) and the liquidus temperature (T_(liq)) is atleast +10° C.
 20. The glass fiber reinforced composite material of claim17, wherein the matrix material is a cementitious materials selectedfrom the group consisting of cement, concrete, mortar, gypsum, slag andcompounds formed by the reaction between lime, silica and water.
 21. Theglass fiber reinforced composite material of claim 17, wherein thematrix material is a thermoplastic selected from the group consisting ofpolyolefins, polyesters, polyamides, polyurethanes and blends thereof.22. The glass fiber reinforced composite material of claim 17, whereinthe matrix material is a thermoset such as polyesters, phenolic resins,epoxy resins, polyacrylics and blends thereof.
 23. The glass fiberreinforced composite material of claim 17, wherein the fiber comprises:2.5-5.5 mol % K₂O; and 5-10 mol % Na₂O.
 24. The glass fiber reinforcedcomposite material of claim 17, wherein the fiber comprises: 1.5-5.5 mol% Li₂O.
 25. The glass fiber reinforced composite material of claim 17,wherein the fiber comprises: 3 to 8.5% CaO.
 26. The glass fiberreinforced composite material of claim 17, wherein the Li₂O/R₂O andK₂O/R₂O molar ratios are ≦0.5.